Safety blasting explosive



Patented July 29, 1941 SAFETY BLASTING EXPLOSIVE Robert David John Owens, Saltcoats, Scotland,

assignor to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application August 9, 1938, Serial No. 223,945. In Great Britain August 17, 193':

' 8 Claims.

The present invention relates to blasting explosives, suitable for use in coal mines especially in atmospheres of a fiery or dusty nature, of the kind in which a blasting cartridge is provided with a sheath or covering containing one or more materials capable of quenching or cooling the flame of the explosive. The effectiveness of the sheath depends on the blanketing of the whole of the exposed longitudinal surface of the cartridge with the cooling material. Many of the particularly effective cooling materials, for example sodium bicarbonate, are loose powders having little or no caking tendency; consequently the packing of the material into the form of a sheath that will satisfactorily withstand transport and handling is an operation of some difiiculty or inconvenience.

Various suggestions have been made in the past such as incorporating a cooling salt with a fibrous pulp and forming it into a paper or incorporating it with chlorinated naphthalene wax,

but such methods have the disadvantage of being either expensive to operate or of employing expensive materials, or else give unpleasant fumes after the explosion of the charge.

This invention has as an object to devise an economical method of manufacturing cooling sheaths for blasting explosives. A still further object is to provide new and cheaper cooling sheaths for blasting explosives, Further objects will appear hereinafter. These objects are accomplished by the following invention.

I have now found that, provided oxidising agents are not present in the sheathing material, bitumen or bituminous composition may be employed in sufiicient proportion to bond the cooling material into a permanently coherent sheath without markedly diminishing the flamequenching or cooling properties of the safety material, and without causing the formation of an objectionable amount of fume after the explosion of the sheathed cartridge.

According to the present invention, a sheathing material for blasting explosive cartridges consists of a composition which is permanently coherent and self-supporting at ordinary temperatures but capable of being worked as a plastic at raised temperatures, and comprises in the absence of oxidising agents a cooling salt, and, as a binder therefor, bitumen and if desired one or more additional substances having the effect of reducing the brittleness of the bitumen at ordinary temperatures.

In putting the invention into effect, the cooling portion of bitumen or bituminous composition to make the mixture plastic underpressure at a temperature at which the bitumen is at least pliable, and the mixture is formed into a sheath at such a temperature.

In forming the sheathing material, 'I prefer to incorporate the bituminous composition thoroughly at a raised temperature, and then add the cooling salt in portions until the whole has been uniformly mixed. The final composition is preferably sheeted by passage through rollers, conveniently by passage in contact with a sheet of fireproofed wrapping material, and may be wrapped round a blasting cartridge while still warm. The composition may also be extruded into fiat sheets or hollow cylinders, and the shaped material may then be chilled after it has been given its final form.

The use of any commercial grade of bitumen is practicable; but I prefer to use a grade having a standard penetrometer test of approximately 200-220. The penetrometer test is the standard test laid down by the Institute of Petroleum Technologists Method A 18 (1929).

- salt is mechanically mixed with a sufficient pro- This test consists in placing the point of a needle 1.0 mm. thick and 50.0 mm. long, tapering for the last 5.0 mm. of its length to a width of 0.16 mm., against the surface of the material to be tested. The needle is weighted to grams, and the material is maintained at a temperature of 25 C. The full weight of 100 grams is permitted to bear on the needle for five seconds and the distance through which the needle penetrates into the material in this time is then measured. This distance expressed in tenths of a millimetre gives the penetrometer number.

If sodium bicarbonate, which decomposes when heated above 100 C. is used, it is necessary to use a bitumen or bituminous composition that is workable at a temperature below 100 C. On the other hand, the softening point of the composition must not be so low that a sheath made therefrom will tend to lose its form at any temperature likely to be encountered by a sheathed cartridge during storage or use. The bitumen or bituminous composition should therefore be capable of retaining its form at temperatures up to 40 C.

The proportion of bituminous composition to be incorporated with the sodium bicarbonate need not exceed 10% of the whole, and usually 5% will be found suflicient to give good results.

The invention is further illustrated by the following examples in which the parts are parts by weight.

Example 1 A mixture of 90 parts sodium bicarbonate, 8 parts of bitumen (penetration 200-220) and 2 parts of gutta-percha resin is introduced into a hot-water jacketed incorporating machine and is worked together at a temperature of 70 C. until a homogeneous plastic mass is obtained. The mass is rolled between rollers on to a strip of fireproofed manila paper, of a width equal to the length of the cartridge which is to be sheathed. The thickness of the coating is about V8" and the coated paper is cut into lengths slightly greater than the circumference of the cartridge. Before the mixture has congealed, oz. cartridges of Polar Saxonite wrapped in thin waxed manila paper, and having an overall diameter of 1%", are wrapped inside the strips with the fireproof paper backing outermost, and

the wrapped cartridges are finally dipped in wax;

The thickness of the coating is such that the 5 oz. cartridges are associated with about 1.5 oz. of the composition.

The wrapped cartridges of this example may be fired in a dangerous mine atmosphere without causing an ignition.

Example 2 A mixture containing 93 parts sodium bicarbonate, 3.2 parts bitumen (penetration 200-220), 2.4 parts smoked rubber and 1.4 parts parafiin wax is worked to form a plastic mass at 70 C., and is extruded in the form of a tube, the wall of which is about Va" thickness, over a former under pressure while still plastic. When the tube is' cool, it is cut into pieces of the required length into which are slipped 5 oz. cartridges of the explosive Polar Saxonite wrapped in thin waxed manila paper. The sheathed cartridges are then wrapped in fireproofed manila paper and are dipped into wax. As in Example 1, the weight of the composition associated with each 5 oz. cartridge is 1.5 oz. A layer of the composition 0.05" thick weighs 6 oz. per sq. foot; an equal volume of 30-50 mesh sodium bicarbonate weighs 3.9 oz.

The wrapped cartridges of this example may be fired in a dangerous mine atmosphere without causing an ignition.

Example 3 The coated paper is then cut into portions of suitable size for wrapping blasting cartridges.

-The bitumen maybe used alone, or in association with other materials, for example guttapercha resin, smoked or crepe rubber, paraffin wax or gelled castor oil, which are adapted to reduce the brittleness of the bitumen at ordinary temperatures.

Other cooling isalts may be used instead 0! sodium bicarbonate; but as a rule it may not be possible to make a satisfactorily tough sheathing material without a notable increase in the proportion of binder used. For example, potassium sulphate may be substituted for sodium bicarbonate in the examples of this specification; but where anhydrous sodium carbonate is used, about 15% of plastic binder will be found desirable, and for calcium fluoride about 20% on the total composition.

This invention is a valuable advance in the art as the new sheaths can be made of inexpensive apparatus and without the use of expensive raw materials; the resulting sheaths are as effective as other sheaths made in other manners and do not cause unpleasant fumes after the explosion.

As many apparently widely difierent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof, except as defined in the appended claims.

I claim:

1. An explosive cartridge adapted for use in gassy mines, said cartridge comprising an explosive charge within a paper container, and a coherent, self-supporting sheath wrapped about said container, said sheath comprising a cooling salt and bitumen and being free from oxidizing agents, said cooling salt being present in substantially greater amount than the bitumen.

2. An explosive cartridge adapted for use in gassy mines, said cartridge comprising an explosive charge within a paper container, and a coherent, self-supporting sheath wrapped about said container, said sheath comprising a cooling salt and bitumen and being free from oxidizing salts, said cooling salt being present in substantially greater amount than the bitumen which is' present in quantities not exceeding 20% by weight.

3. An explosive cartridge adapted for use in gassy mines, said cartridge comprising an explosive charge within a paper container, and a coherent, self-supporting sheath wrapped about said container, said sheath comprising from to by weight of a coolingsalt, not more than 20% by weight of bitumen, and a. cohesion promoter for said bitumen, said sheath being free from oxidizing agents. 7

4. The explosive cartridge of claim 3, wherein the cooling salt is sodium bicarbonate.

5. The explosive cartridge of claim 3, wherein the cohesion promoter comprises a rubber composition.

6. The explosive cartridge of claim 3, wherein the cohesion promoter comprises jelled castor oil.

7. The explosive cartridge of claim 3, wherein a the cohesion promoter comprises paraflin wax.

. of a cohesion promoter, said sheath being tree from oxidizing agents,

ROBERT DAVID JOHN OWENS. 

